The Turbocharger: More Than Just Boost
We’ve established that the engine needs to know how much air is available.
But knowing how much air is available is only half the job.
The next question is:
How do we get more air into the engine when we need it?
That’s where the turbocharger comes in.
Most people understand the basic idea of a turbo:
Exhaust gases spin a turbine, which is connected to a compressor. The compressor forces more air into the engine.
And that’s correct.
But on a modern diesel engine, the turbocharger is doing far more than simply making boost.
The ECU uses the turbocharger to help control:
- Airflow
- Boost pressure
- Combustion
- EGR flow
- Emissions
- Engine performance
- And, under certain conditions, even exhaust temperature
This is especially true with a variable geometry turbocharger (VGT).
But… before we get into VGTs, we need to understand something very simple:
Why does an engine need a turbocharger in the first place?
A naturally aspirated engine can only draw in as much air as atmospheric pressure and the engine’s own pumping action can provide.
A turbocharger changes that.
Instead of simply allowing the engine to breathe, the turbocharger can push more air into the cylinders.
More air means we can burn more fuel while still maintaining the correct air/fuel conditions for combustion, and that means more power.
But there’s an important point here:
The turbocharger doesn’t create power.
The fuel creates the energy.
The turbocharger simply allows the engine to get more air so that it can burn more fuel efficiently.
And this is where things start getting interesting.
Because on a modern diesel, the ECU isn’t just asking:
“How much boost do I want?”
It’s asking something much more complicated:
“How much air do I need, and how do I get it there?”
That distinction is extremely important when diagnosing turbocharger problems.